Fabrication of bio-polymer-based hydrogel for methylene blue remediation: Kinetics, mechanisms, and environmental implications

ABSTRACT Due to the presence of highly persistent and non-biodegradable dyes that are capable of causing harm to people, plants, animals, and the environment, the treatment of dye-contaminated water tends to be highly challenging. In the current work, polyacrylic acid and bio-polymer-based hydrogels of hydroxyl ethyl cellulose (HEC) were prepared through the free radical polymerization method and were used as adsorbents for the adsorption of methylene blue (MB). To estimate the nature and mechanism of adsorption, kinetics, and isotherm models were adopted. Pseudo-second-order kinetic model was followed by the sorption of MB. Results demonstrated that with an increase in concentration of dye dosage, adsorption increases linearly. Freundlich isotherm model was followed for the sorption of MB onto polyacrylic acid and bio-polymer-based hydrogels. Thermodynamic study of the adsorption process reveals that the adsorption process was spontaneous and endothermic as inferred from Gibbs free energy and enthalpy values of 33.08 kJ/mol and 3.83 kJ/mol at 303K, respectively. Recycling performance was tested and inferred that bio-polymer-based hydrogel having 0.6 gm. Hydroxyethyl cellulose decreases its adsorption efficiency equivalent to 5% after consecutive five cycles. The bio-polymer-based hydrogels will be used as an effective adsorbent for removing cationic dyes from wastewater on an industrial scale.